The invention relates to computerized devices including rangefinders for ballistic trajectory compensation of small arms.
U.S. Pat. No. 4,531,052, issued in 1985 to Moore, involves a computerized rifle telescopic sight with a stadia rangefinder for ballistic trajectory compensation. The rangefinder is a dynamic stadia rangefinder, with the rangefinding bracket lines being produced by solid state imaging of LCD or LED devices, the stadia brackets being optically superimposed on one of the focal planes of the scope. The size of the target is inputted into the computer, the current scope magnification (if it is a variable power scope) is inputted, and the hunter has merely to operate the controls to adjust the brackets to precisely frame the top and bottom of the segment (usually shoulders to chest) of the target animal that is the stadia reference, and the computer will output the range as per well known stadia rangefinding formulae, Moore's device utilizes a small arms ballistic trajectory program relying on such familiar methods of computation as the Siacci method, together with data inputting buttons, and data inputting solid state display. The hunter inputs ballistic data specific to his rifle and the ammunition he is using, such as bullet weight, muzzle velocity, ballistic coefficient; sighting adjustment data, such as zero range and height of scope; atmospheric data and angle of elevation. This inputted data together with the stadia rangefinder determined range to the target is utilized by the computer in applying the ballistic trajectory program to determine what adjustments have to be made to the aiming mark (usually the center of the crosshairs reticle of the scope) to compensate for range and other parameters involved so that the hunter can aim the firearm precisely where he wants the bullet to hit the target and have it impact the target at that point. The computer moves one of the bracket lines to the appropriate point on the verticle line of the crosshair, so that the intersection of that bracket line and the verticle line of the crosshair constitutes the correctly compensated aiming point. The hunter, using this compensated aiming point supplied by the computer, is now in a position to aim "dead on" and fire, the uncertainties of guesswork and holdover having been eliminated. In U.S. Pat. No. 4,777,352, issued to Moore in 1988, he discloses a variation of his device in which in place of the solid state imaged brackets, a computer controlled cam moves a physical reticle containing a horizontal bracket line with the second stationary bracket line being the horizontal line of the crosshairs reticle. In U.S. Pat. No. 4,965,439, issued to Moore in 1990, he discloses a refinement in which a computer controlled screw displaces the spring biased erector tube containing the scope crosshairs reticle in the rear focal plane of the scope so that its horizontal line moves in relation to a second reticle in the front focal plane in front of the erector tube which contains the other stadia bracket line which remains stationary. The use of the digital computer together with the small arms ballistic trajectory program and broad data inputting capability make Moore's device a major advance over the prior art of mechanical bullet drop compensation/stadia rangefinding rifle scopes, deliniated in some detail in the "Description of the Prior Art" section in Moore's patents, in which only a small number of ballistic trajectories, not modifiable for unique ammo, rifle, sighting in, atmospheric, etc., conditions can be accomodated with interchangeable bullet drop compensation elevation knobs (or overlays for the elevation knobs) each calibrated to a particular ballistic trajectory.
U.S. Pat. No. 4,561,204, issued to Binion in 1985, discloses a computerized rifle telescopic sight with a stadia rangefinder for ballistic trajectory compensation. In the Binion invention, the computerized solid state reticle display, showing the stadia brackets, computer controlled aiming mark, and range and atmospheric data, is offset laterally by a connecting arm from the scope to which it is connected, and the offset arm is so adjusted that the shooter looks through the scope with one eye, while viewing the computer controlled reticle display with the other eye. Superimposition of the reticle display on the scope field of view is by the combining of the two images in the hunters optical central nervous system, rather than by optical superimposition within the scope. Binion discloses the use of sensors for wind, temperature, humidity, and muzzle angle of elevation. In addition to the illustrated stadia rangefinder, Binion suggests that his device could be designed without a rangefinder, with simply the means to input range data to be determined by a separate rangefinder. Although Binion illustrates his device with knobs for adjusting the aiming mark vertically and horizontally for sighting in the rifle, his invention, unlike Moore' s, does not include a data inputting button console for inputting ammo, rifle, sighting in, or any other data.
Binion's device has many weaknesses, in comparison to Moore's. First, the absence of plurality of ammo, rifle, and sighting in data inputting capability severely restricts the usefullness of the device for civilian purposes, and in effect dictates that the costly expedient of producing the device in different models programmed for particular rifle-ammo combinations be utilized. A second very serious defect, which renders the device worse than useless in the field is that the two eye method of combining the images of the scope field of view and the reticle display in the hunter's optical central nervous system, produces an unstable superimposition in which the perceived image fluctuates from the combination of the two images to the image of the reticle display to the scope field of view, back to the combined image, etc. This kind of unstable image results from "tricking" the optical nervous system, by having the separate eyes seeing completely different images, rather than looking at the same image. A third serious defect is that the shooter's field of view is restricted to that of the telescopic sight. At high scope magnification, the scope field of view can be very narrow. If the animal moves, the hunter will loose sight of him. With the Moore device, or with a standard rifle scope, the second eye of the hunter not looking through the scope is available for seeing a broad, unmagnified field of view. Another serious problem with the Binion device is that its laterally offset position from the scope renders it very vulnerable to being knocked out of precise alignment with the scope in normal field use, which would result in gross inaccuracy in the use of the device, until it was realigned with the scope. The two eye reticle image superimposition system, which is the keystone of the Binion device, is very impractical and undesirable.
U.S. Pat. No. 4,787,739, issued to Gregory in 1988, discloses, inter alia, a computerized rifle scope with a stadia rangefinder for ballistic trajectory compensation, in which the central feature of the Gregory invention is that the computer generates a solid state display of an actual outline of the target or some part of the target rather than mere bracket lines. Both static and dynamic stadia rangefinders of this unusual type are disclosed. Data inputting of specific: ammo, rifle, sighting in, atmospheric, etc. data is not included in the Gregory patent. Gregory's device is primarily a very innovative system for stadia rangefinding as part of a computerized, artificial "vision" system, and only secondarily a computerized rifle scope with a stadia rangefinder for aiming mark adjustment as per ballistic trajectory at determined range. For this secondary purpose, aside from its grossly inadequate data inputting for ballistic trajectory compensation, it has several serious weaknesses. In the first place, for the computer to produce accurate full target (or part of target, i.e., the head) outlines, very complex, memory hungry programing will be required as well as very expensive electronic imaging hardware to provide a very fine, high resolution image of the complex outline. This will be very costly, and will leave little data processing capability in a very small computer included in a small arms scope for ballistic trajectory programming, etc. Second, the computer generated target outline will be worse than useless, unless the target profile that the hunter sees is that outlined. Gregory illustrates the side profile of a deer in various examples from his drawings. What if the deer is facing forward or rearward or at an angle?. Finally, the complex target outline, even in the dynamic stadia rangefinder embodiment, where only a single outline is shown at one time, produces intolerable, distracting clutter in the hunter's field of view.
The stadia rangefinding systems used to input target range in the Moore, Binion, and Gregory computerized small arm scopes have the same inherent flaw as the stadia rangefinding systems used in the prior art of mechanical bullet drop compensation/stadia rangefinding small arms scopes when applied to living creatures, namely, that living creatures are not of a fixed size, but to the contrary, show wide size variation. Moore himself in U.S. Pat. No. 4,777,352 (col. 12, lines 17-37) states that the shoulders to chest measurement of deer can vary from an alleged norm of 18 inches to 22 inches because of good forage. Presumably, if forage were poor, the reverse would be true, and the measurement might be 14 inches. This, of course, constitutes a very wide stadia reference size variation, which would produce gross inaccuracy in the rangefinding. Moore, however, is satisfied that visits to taxidermists and hunting supply stores will result in correct stadia reference size inputting. Biological facts point to a different conclusion. Size variations among adult creatures of a given sex of any species, mule deer, grizzly bears, or human beings, are caused by many factors in addition to forage, including, inter alia, genetics, condition of the mother following conception, condition of the mother during the nursing period,disease history of the individual. It is these factors, among others, which produce such wide size variation among a given species population during a season of any given forage conditions. These are rudimentary biological facts. Indeed, it is interesting to note that even the major manufacturers of rifle scopes containing a stadia rangefinding feature are in disagreement over the size norm for the stadia reference for given animals. Thus, Leupold & Stevens takes the position that shoulders to chest for a deer is 16 inches, Bushnell states in its brochure that it is 18 inches, while Tasco in its brochure argues that for a white tail deer it is 18 inches but for a mule deer it is 22 inches. Just as it is common knowledge that adult human males do not come in a fixed size, but instead come in a wide variety of sizes, so it also is for a given sex and age with any other animal species.
Thus, it is seen that the utilization of stadia reference size norms for animals is a striking example of the microcomputer acronym, "gigo", which stands for "garbage in, garbage out", and which means that if flawed data is inputted into the computer, the outputted data is certain to be flawed. Exactly how flawed the outputted data (aiming mark adjustment to achieve ballistic trajectory compensation at the determined target range) is likely to be will now be examined. Three very popular rifle calibers used for deer and deer size game are considered, the 7 mm Remington Magnum, the 270 Winchester, and the 30--30 Winchester. Federal Cartridge Co. factory leaded ammunition is utilized, specifically the 7 mm Remington Magnum 165 gr spitzer boat tail, the 270 Winchester 150 gr spitzer boat tail, and the 30--30 Winchester 170 gr Nosier round nose. Published Federal firing table data is utilized. Analysis has been carried out with the Barnes Ballistics program. Assuming that the stadia reference (shoulders to chest) norm for deer is 18 inches, and a size variation of 16-20 inches is allowed, the rangefinding error margin is .+-.11%, which for purposes of this analysis will be dealt with as .+-.10%. Assuming that the size variation is 14-22 inches, the rangefinding error margin is 22%, which for purposes of this analysis will be dealt with as 20%.
For a deer size target, the lethal zone (also called the "vital zone" and the "point blank zone") is considered to be .+-.5 inches; i.e., if the bullet point of impact deviates no more than that amount from the point of aim, a kill is likely; if the bullet point of impact deviates more than that amount from the point of aim, a miss is likely. Thus it is clear that for a deer size target, the stadia rangefinder extends lethal accuracy no further than that range at which a given rangefinding error (resulting from actual target size deviation from the inputted stadia rangefinding target size norm) translates into bullet impact deviation from point of aim no greater than .+-.5 inches. For the Federal 7 mm Rem Magnum ammo, a 10% rangefinding error limits the range of lethal accuracy to approximately 350 yards. With a 20% rangefinding error, lethal accuracy is limited to approximately 265 yards. For the Federal 270 Winchester ammo, a 10% rangefinding error limits the range of lethal accuracy to approximately 340 yards, while a 20% rangefinding error limits lethal accuracy to about 250 yards. For the Federal 30--30 Winchester ammo, a 10% rangefinding error limits lethal accuracy to 250 yards, while a 20% rangefinding error limits lethal accuracy to about 200 yards. Even with the optimistic 10% rangefinding error, with each of the three types of ammo, the range of lethal accuracy achieved with the stadia rangefinder is no more than maximum point blank range. Maximum point blank range for the Federal 7 mm Remington Magnum ammo is 366 yards with optimum zero range of 309 yards; maximum point blank range for the Federal 270 Winchester ammo is 346 yards for an optimum zero range of 293 yards; maximum point blank range for the Federal 30--30 Winchester ammo is 250 yards for an optimum zero range of 214 yards. With a more realistic 20% rangefinding error, maximum point blank range is substantially greater than the range of lethal accuracy provided by the rangefinder.
The computerized devices developed by Moore, Binion, and Gregory, however great the data processing capability of the computer, however powerful the ballistic trajectory program, however great the scope and detail of data inputting capability, are incapable of providing greater accuracy than the stadia rangefinding systems that they use, and this is their fatal weakness. Even with an unrealistically optimistic assumption of only a 10% stadia rangefinding error, the computerized devices of Moore, Binion and Gregory are worthless and a waste of money for the hunter because the hunter can utilize the cheap, simple, and reliable expedient of sighting in his rifle to maximum point blank range to achieve the same range of lethal accuracy. If a more realistic 20% stadia rangefinding error is assumed as a result of actual target size deviation from the inputted stadia rangefinding target size norm, the hunter finds his range of lethal accuracy degraded substantially by the computerized devices from maximum point blank range. The stadia rangefinder, which is an integral part of Moore's and Gregory's devices, and which is the illustrated rangefinder with Binion's device (although Binion does allow for the use of an external rangefinder with range data inputting capability for his device), renders these devices worthless shams in terms of the inability to achieve any increase of lethal accuracy range over maximum point blank range, and prevents the microcomputer, with broad data inputting capability, and with powerful small arms ballistic trajectory compensation programs such as Barnes Ballistics, from achieving the theoretical potential of substantial extension of lethal accuracy range far beyond point blank range.
There are only two alternative rangefinder systems to the stadia rangefinder for small arms, the laser rangefinder and the triangulation rangefinder. The laser rangefinder is widely used in ordnance fire control systems. However, the laser rangefinder's size, weight, and cost alone preclude it from consideration for small arms ballistic trajectory compensation. In addition, a sufficiently powerful laser for rangefinding out to 1,000 yards and beyond, presents dangers (i,e., to the eyes), and is illegal for civilian use. It is the triangulation rangefinder which provides the needed accuracy in a sufficiently small and cheap package,
The triangulation rangefinder is an optical instrument for measuring distance to a target comprising two windows, each with a reflector, spaced apart, through which light from the target enters. The distance between the centers of the windows is the base length of the triangle, and the rangefinder operates as an angle measuring degree for solving the right triangle comprising the triangle base and the lines from the two windows to the target. Such rangefinders have been in use for more than a century, and those knowledgeable in the prior art of triangulation rangefinders will be familiar with a variety of types, including the coincidence (single eye view) type, with merger of images, split images, superimposed images, use of mirrors (with one of the mirrors being a beam splitter) or prisms as reflectors, and also stereoscopic types. In the simple coincidence type, there are two reflecting elements, one of which is displaced to form the angle with the target to be measured, or alternatively, the two reflecting elements may both be fixed in position and a displacement prism may be utilized to displace the image of one to form the angle with the target. Such rangefinders, and the mathematical formulae utilized for solving the triangles are described in some detail in D. F. Horne, Optical Instruments and their Applications, 1980, and in "Rangefinder (optics)" by Edward K. Kaprelian on pp. 186-188 of vol. 15 of the McGraw Hill Science Encyclopedia, 6th ed., 1987.
The seminal triangulation rangefinder patent is British Pat. No. 9520, issued to Archibald Bart and William Stroud in 1889. The triangulation rangefinder was invented by Barr & Stroud to satisfy an advertisement by the British War Office for an accurate rangefinder for use by infantry. Their coincidence triangulation rangefinder is as described in the previous paragraph, Bart & Stroud also disclose in the patent the use of a swivel clip to attach the rangefinder to a rifle, allowing it to be swiveled perpendicular to the rifle for use, and above and parallel to the rifle barrel when not in use. The proposed attachement to the rifle is very cumbersome, bulky, gets in the way of the rifle sight (and is thus impractical), and will subject the sensitive optical instrument to the severe shocks of recoil which will throw off the rangefinder's calibration. There is no bullet drop compensation feature, and the user would be manually adjusting the rear sight of the rifle to conform to the deterimed range. This is very slow, cumbersome and crude integration with a firearm, and furthermore, its data output capability is limited to range.
U.S. Pat. No. 3,737,232, issued to Raymond Milburn in 1973, is for a triangulation rangefinder for small arms comprising a telescopic sight and a laterally connected "range telescope" In this triangulation rangefinder, the shooter views through one eye the reticle in the telescopic sight and through the other eye the reticle in the range telescope. A rotatable wheel moves a lense assembly in the range telescope, which optically displaces the image of the reticle in that telescope. The device is so calibrated that when the marksman has moved the two crosshairs reticles to coincidence, the range to target can be read on a scale on the rotatable wheel.
The Milburn triangulation rangefinder has numerous weaknesses. First, it is a very cumbersome device which would consume precious time in utilization, in which time the target might wander off. Second, both eyes of the shooter are utilized, which means that the shooter's field of view is limited to the narrow field of view of the telescopic sight, which could be most unfortunate if the animal should quickly move out of the field of view of the scope. Thirdly, the device would cause the rifle to be very bulky and cumbersome to carry and manipulate in the field. But the most serious flaw relates to the accuracy of the device itself. The accuracy of a triangulation rangefinder is a function of the magnification of the target images and the length of the triangulation base. In this case, the base is the distance between the centers of the two scopes. The rifle, with this device attached, would be totally unwieldy, and extremely difficult to carry or manipulate in the field, unless this lateral distance from the scope to the range telescope is kept as short as possible. Even a 6 inch lateral extension would be very cumbersome, and render the rifle very difficult to carry or use in the field. But, even with high magnification, i.e., 18 power, a triangle base of more than twice that length (i.e., at least one foot) would be required to increase the range of lethal accuracy to approximately twice maximum point blank range. The inherent flaw, which renders this device impractical and unusable for its stated purpose-accurate rangefinding for a firearm--is that there is a direct conflict between one of the requirements of accurate triangulation rangefinding (a long triangulation base) and one of the requirements of easy field carrying and fast and easy field manipulation (a compact device with negligible lateral offset) of the weapon.
Ranging, an unincorporated division of Crossman Corporation, manufactures the Rangematic 1000 triangulation rangefinder, which, with its five interchangeable Distran representative ballistic trajectory scales, increases the range of lethal accuracy beyond maximum point blank range for some types of rifle ammo, when fired under "standard" conditions, by about 50%. This is a considerable improvement over the stadia rangefinding/bullet drop compensation rifle scopes, which offer no increase in range of lethal accuracy over maximum point blank range because of the inherent inaccuracy of the stadia rangefinding system when applied to living targets. The Rangematic has a triangulation base of 9 inches and a magnification of 6 power.
The formula for determining the accuracy of a triangulation rangefinder is 2(U.O.E.)=2(58.2R.sup.2 /BM). 2(U.O.E.)=the rangefinding error in yards, covering 95% of such rangefinding error. R=range in 1000 yard units. B=triangulation base in yards. M=magnification. Utilizing this formula, with the parameters of the Rangematic 1000, together with the Barnes Ballistics program, with the same Federal hunting ammunition used, supra, in determining the effect on the accuracy of ballistic trajectory compensation of the inaccuracy of stadia rangefinding applied to living targets, the following results are achieved: (1) the 7 mm Rem. Magnum has its range of lethal accuracy on deer sized game increased from a maximum point blank range of 366 yards to 540 yards, only 9 yards less than a 50% increase; (2) the 270 Win. has its range of lethal accuracy increased from a maximum point blank range of 346 yards to 500 yards, only 19 yards less than a 50% increase; (3) the 30--30 Winchester has its range of lethal accuracy increased from a maximum point blank range of 250 yards to 400 yards, 25 yards more than a 50% increase. This is a very impressive increase in the range of lethal accuracy as a result of triangulation rangefinding with an over the counter triangulation rangefinder, when compared to the abysmal results of stadia rangefinding, supra.
It is to be emphasized that the 50% increase in range of lethal accuracy has been achieved utilizing the Barnes Ballistics program, which allows for precise data inputting so that the ballistic trajectory is specific to particular ammo, etc. The Distran interchangeable bullet drop compensation scales (like the interchangeable bullet drop compensation elevation knobs discussed, supra, with respect to mechanical stadia rangefinding/bullet drop compensation scopes), because they offer only a very limited number of representative ballistic trajectories, and because they are not modifiable for specific field conditions, give a much lower level of accuracy. The Federal 7 mm Remington Magnum ammo is not represented in the "scale selector chart". Sticker 5 is close in bullet drop figures to this specific ballistic trajectory, but only at 50 yard intervals from 200 yards to 500 yards. However, even with this ultra-fiat trajectory ammo, with range intervals of 50 yards, bullet drop differential over the 50 yard intervals ranges from 6-9 inches at ranges from 300 to 500 yards, I.e,. the computer program (or very laborious and time consuming computation) must be used to provide a custom ballistic trajectory table at 20 yard intervals, so that bullet drop deviation is kept within the .+-.5 inch deviation limits required for lethal accuracy against deer size game. For the Federal 270 Win. ammo used, the problem is similar. Once again, the ammo used is not shown on the "scale selector chart", although sticker 7 approximates the ballistic trajectory. Bullet drop differentials of 12 inches are the result of the 50 yard intervals on the scale at ranges from 300 to 500 yards. Again, the computer program must be used to reduce the intervals to 20 yard intervals, and achieve the 50% increase in the range of lethal accuracy. With the 30--30 Winchester, the results are much worse, the scale sticker suggested for the 30--30 is not at all representative of its ballistic trajectory, so that the computer program is even more necessary. The interchangeable Distran scales offer only a small number of "representative" ballistic trajectories, and present, in fact, a very crude and inaccurate approximation of any given actual ballistic trajectory, even under "standard conditions". This crude and inaccurate manual system of bullet drop compensation does not even purport to offer any help if field conditions (i.e., temperature, wind, elevation, muzzle inclination, zero range, sight height, etc.) in the field vary from the hypothetical "standard conditions", as they almost always will. To achieve a level of accuracy in ballistic trajectory compensation commensurate with the high level of rangefinding accuracy of the Rangematic 1000, the hunter would have to carry into the field a portable personal computer, loaded with a small arms ballistic trajectory program such as Barnes Ballistics, together with appropriate instruments, such as an annemometer for crosswind determination, a level for muzzle inclination determination, etc. This is obviously ludicrous, since the expenditure of time involved in utilizing this equipment in the field, and making the appropriate adjustments to the scope, would result, more often than not, in the trophy wandering away long before the individual was ready to fire.